This investigation will be concerned with the study of the sulfated mucopolysaccharides that we have demonstrated are synthesized add secreted by endothelial cells raised in tissue culture. Primary cultures and established lines of endothelial cells from rabbit aorta will be used. S35-mucopolysaccharides will be examined by electrophoresis on cellulose acetate and subjected to enzymatic degradation with different chondroitinases and chondrosulfatases; the breakdown products will be analyzed by chromatography on paper. The characterization of the sulfated species synthesized by the endothelial cultures may help to define a functional marker for the endothelial cells that can be used to monitor changes in the composition of the cell population. Furthermore, the biochemical characterization of the sulfated mucopolysaccharides is an important prerequisite for future studies aimed at defining their biological role in the whole organism. Possible species differences in the synthesis and secretion of sulfated mucopolysaccharides, which have been suggested by pilot studies, will also be investigated.